In accordance with the miniaturization of semiconductor elements, the shortening of the wavelength of an exposure light source and the realization of high numerical apertures (high NA) for projector lenses have been promoted. For achieving the enhancement of resolving power by further wavelength shortening, it is heretofore known to employ a method in which the space between a projector lens and a sample is filled with a liquid of high refractive index (hereinafter also referred to as an “immersion liquid”), generally called a liquid-immersion method. The liquid-immersion method is effective in all pattern shapes. Further, this method can be combined with a super-resolution technology, such as a phase shift method or a modified illumination method, now under study.
Since the emergence of the resist for a KrF excimer laser (248 nm), it has been of common practice to, in order to compensate for any sensitivity deterioration caused by light absorption, employ an image forming method through chemical amplification as a resist image forming method. Brief description of a positive image forming method through chemical amplification is given below by way of example. Upon exposure, an acid generator is decomposed in exposed areas to thereby generate an acid. At the bake after the exposure (Post-Exposure Bake: PEB), the generated acid is used as a reaction catalyst so that an alkali-insoluble group is converted to an alkali-soluble group. Thereafter, alkali development is carried out to thereby remove the exposed areas. Thus, the relevant image forming method is provided.
The resist for an ArF excimer laser (193 nm) utilizing this chemical amplification mechanism is now becoming mainstream. However, in the application of liquid-immersion exposure, the resist has been unsatisfactory in not only the problem of pattern collapse such that a formed line pattern collapses to thereby cause a defect in device production but also the line edge roughness involving roughening of pattern side walls.
Moreover, it is pointed out that when such a chemically amplified resist is applied to liquid-immersion exposure, as the resist layer is brought into contact with the immersion liquid during the exposure, not only would the resist layer suffer a property alteration but also components having an unfavorable influence on the immersion liquid would leach from the resist layer. In this connection, patent references 1 to 4 describe examples of inhibiting the leaching by the addition of a resin containing a silicon atom or a fluorine atom.
Patent reference 5 discloses a resist loaded with a specified polymeric compound containing a fluorine atom and a lactone structure as a resist material being less in a shape change between dry exposure and liquid-immersion exposure to thereby excel in process applicability.
Further, patent references 6 and 7 disclose photoresist compositions each comprising a block copolymer containing a specified repeating unit as a photoresist composition appropriately used in liquid-immersion exposure.
Furthermore in the liquid-immersion exposure process, in the event of exposure using a scan type liquid-immersion exposure machine, the exposure speed is decreased when the immersion liquid fails to move while tracking a moving lens. This would negatively affect productivity. When the immersion liquid is water, it is preferred for the resist film to be hydrophobic from the viewpoint of superiority in water tracking property.
However, even when the liquid-immersion exposure is carried out using the above-mentioned technologies, it is still required to further reduce the occurrence of development defects and scum.